(CNN) -- On the first day of the national Veterans of Foreign Wars convention in Kansas City, Missouri, Sens. Hillary Clinton and John McCain offered widely differing views on the Iraq War.

Speaking to the VFW Tuesday, Sen. John McCain said a defeat in Iraq would be "catastrophic."

The two presidential candidates addressed the same audience of veterans -- and both received applause.

"I think that it's unacceptable for our troops to be caught in the crossfire of a sectarian civil war while the Iraqi government is on vacation," said Clinton, a New York Democrat. She said that the best way to honor the service of U.S. troops would be to bring them home.

McCain, whom Clinton honored for his service in Vietnam and noted their travels in Iraq and Afghanistan, cautioned against such a withdrawal.

Gen. David Petraeus, the top military commander in Iraq, also addressed the convention by way of videotape.

Sen. Barack Obama, D-Illinois, and former Sen. Fred Thompson, R-Tennessee, will address the convention Tuesday. Obama is seeking the Democratic presidential nomination, while Thompson is expected to officially declare his intention to seek the GOP nomination after Labor Day